Among known morphine-like peptides, beta-endorphin, with an amino acid sequence corresponding to residues 61-91 of ovine beta-lipotoropin, is most active as an analgesic by injection directly to the brain and is the only one which is active by intravenous adminstration. We propose to synthesize analogs of beta-endorphin by the solid-phase method for the following objectives: (a) enhancement of opiate activity, (b) antagonize opiate activity, (c) determine opiate activity but no narcotic addiction, such as tolerance and physical dependence, (d) determine essential residue(s) in beta-endorphin for opiate activity, (e) determine the importance of metenkephalin in the beta-endorphin molecule by synthesis of the analog beta-endorphin-(6-31).